[Shadow]

How many atoms/molecules make a phase?

[Corribus]

I don't understand the question.

[Shadow]

One molecule can't be liquid. How many molecules are needed for a substance (e.g. HCl) to be called a liquid?

[Corribus]

Congratulations. You've just stumbled into a sorites paradox.

[ad0rian423]

According to this definition of phase http://www.quantachrome.co.uk/en/dictionary/phase.asp:
phase (noun) - a thermodynamic state of matter that has physically distinctive properties in comparison with other states of chemically identical matter

So I guess the non-philosophical response is that it depends on how many atoms are needed to produce a particular chemical property.

[Borek]

So I guess the non-philosophical response is that it depends on how many atoms are needed to produce a particular chemical property.

A friend of mine did (for his masters,back in eighties) QM calculations to find out how the properties of some particular crystal change when it grows, to find out when it can be called "a solid".